1. Field of the Invention.
The present invention relates to a frequency counter, provided with a non-volatile memory such as EEPROM, used in an IC card such as a pre-paid card, and to a frequency counting method using this frequency counter, and particularly to a frequency counter suitable for use where the maximum count frequency is large, or one large frequency is counted at a time, such as in a prepaid shopping card, and to a counting method.
2. Description of the Related Art
Japanese Patent laid-open No. Hei. 7-141478, for example, discloses a conventional frequency counter and counting method for use with an IC card. FIG. 13 is a drawing explaining a frequency counter and frequency counting process of the related art. As shown in FIG. 13(a), the frequency counter and counting process of the related art has an 8-bit fill-in type counter, comprising an electrically rewritable non-volatile memory, such as EEPROM, with multiple stages, and one bit is written in for each frequency count. If one stage has 8 bits filled in, then the next stage will have one bit filled in, as shown in FIG. 13(b). After that, as shown in FIG. 3(c), the fill-in type counter at the stage that is all filled in is cleared to `0`.
The number of guaranteed rewrite operations of an EEPROM is restricted to approximately 10,000. For this reason, the above described frequency counter and frequency counting method of the related art can not be applied to use where the maximum frequency is as large as 100,000, such as in a prepaid shopping card. Also, a frequency counter constructed using EEPROM with a large maximum frequency would be very large. Still further, the above-described method of the related art counts one at a time, which means that when frequency counts from a few hundred to tens of thousands are counted in one go, as in a prepaid shopping card, processing takes a long time.
The present invention is intended to solve the above-mentioned problems of the related art, and an object of the present invention is to reduce the number of times a non-volatile memory is rewritten. A further object is to reduce the number of memory cells of a non-volatile memory for the maximum frequency. A still further object of the present invention is to shorten the count processing time.